1. Field of the Invention
The present invention relates to a method of manufacturing a surface emitting laser element of a vertical cavity type and relates to the surface emitting laser element of the vertical cavity type.
2. Description of the Related Art
Conventional surface emitting laser elements of the vertical cavity type include a plurality of accumulated semiconductor layers. The semiconductor layers include active layers between a reflecting mirror (e.g., a distributed Braggs reflector (DBR)) on the upper side of the semiconductor layers and a reflecting mirror (e.g., a DBR mirror) on the lower side of the semiconductor layers. Moreover, the conventional surface emitting laser elements of the vertical cavity type have the structure of a mesa post and an electrical current narrowing layer in order to control the electrical current path and to enhance the efficiency of the electrical current injection. Further, the electrical current narrowing layers include an electrical current narrowing part that is located at the outer circumference and that is formed of Al2O3, and comprises the electrical current injection part of a round shape that is located at the center of each of the electrical current narrowing parts and that is formed of AlAs. Still further, the electrical current injection parts are the electrical current path in the case where the electrical current is injected into the surface emitting laser element of the vertical cavity type, and the open part allows the laser beam to flow out.
Still further, each of the conventional surface emitting laser elements of the vertical cavity type have the layer for the electrical current path that has lower resistance and that is formed of the semiconductor is a (p+) type at each of the corresponding predetermined locations for each of the corresponding top layers among the plurality of semiconductor layers and between each of the corresponding top layers and each of the corresponding electrical current narrowing layers respectively, in order to perform the injection of the electrical current efficiently from each of the corresponding electrodes of the annular shape at the (p) side. The electrical current that is injected from the electrode of the annular shape at the (p) side thereof is efficiently injected into the active layer via the electrical current narrowing layer by passing through the corresponding layers for the electrical current path. As a result, it threshold electrical current for emission from each of the surface emitting laser elements of the vertical cavity type is reduced. Still further, each of the layers for the electrical current path at each of the top layers of the layers of the semiconductor function as the contact layer that corresponds to each of the electrodes of the annular shape at the (p) side, the “contact layer”.
Light that has a predetermined wavelength for a laser oscillation forms a standing wave at between the two reflecting mirrors in accordance with a surface emitting laser elements of a vertical cavity type. When a standing wave to be formed within the surface emitting laser elements, the standing wave forms a loop between the two mirrors. Still further, the electrical current narrowing layer, the contact layer and the layer for the electrical current path, that are described above, are individual layers designed with a higher priority regarding each of the electrical characteristics so that a laser beam can be absorbed and/or scattered and arranged as a node for a standing wave of light. And the thickness and the index of refraction of each of the layers within the conventional surface emitting laser element can be controlled in order to realize each of the locations of the loop and the node for the standing wave of the light that are described above.
Still further, the conventional surface emitting laser elements of the vertical cavity type that are individually include a re-phase layer on the surface of the contact layer at the inner side of the open part of the electrode of the annular shape at the (p) side. Still further, each of the re-phase layers can formed of the dielectric substance, such as silicon nitride or the like. The re-phase layer can be inserted between the contact layer and the bottom reflecting mirror. Furthermore, the optical thickness can be adjusted to be approximately λ/4, in order to locate each of the contact layers at the node of the standing wave, and each of the corresponding bottom surfaces of the reflecting at the loop of the standing wave. An optical thickness of a layer is expressed by a product of a layer thickness and an index of refraction of the layer.    [Patent Document 1] The U.S. Pat. No. 6,916,672    [Patent Document 2] The U.S. Pat. No. 6,750,071
However, conventional surface emitting laser elements of the vertical cavity type have an increased a threshold electrical current for emission comparing to a design value for the threshold electrical current due to an increased resistance of the element.
Here FIG. 10 is a cross sectional view of a principal part of an exemplary conventional surface emitting laser element of a vertical cavity type. And as shown in FIG. 10, a surface emitting laser element of a vertical cavity type (300) comprises a configuration of: an electrical current narrowing layer (307) that comprises an electrical current narrowing part (307a) which is designed to be located at an outer circumference, and an electrical current injection part (307b) of a round shape which is designed to be located at a center of the electrical current narrowing part (307a); a spacer layer of a (p) type (309); a layer for an electrical current path of a (p+) type (310); another spacer layer of a (p) type (311); and a contact layer of a (p+) type (312), that are accumulated in order one after the other. Moreover, an electrode of an annular shape at a (p) side is formed on the contact layer of the (p+) type (312), and a disk shaped layer for a phase adjustment (314) is formed of a silicon nitride at an inner side of an open part of the electrode of the annular shape at the (p) side (313). Further, an upper DBR mirror (316) is formed on the electrode of the annular shape at the (p) side (313) and on the layer for the phase adjustment (314), comprising a multilayered film layer of a dielectric substance. Still further, an active layer is located at a lower part of the electrical current narrowing layer (307). Furthermore, from the active layer through the contact layer of the (p+) type (312) has a configuration of mesa post as a post shape.
A gap (321) that has a width of approximately between 0.3 μm and 0.5 μm is formed all over an outer circumference of the layer for the phase adjustment (314) between the outer circumference of the layer for the phase adjustment (314) and an internal circumference of the electrode of the annular shape at the (p) side (313). Moreover, a gutter (324) is formed on the contract layer of the (p+) type (312) directly under such the gap (321). The gutter (324) is formed when the mesa post is formed in the surface emitting laser element of the vertical cavity type (300) due to a trespass of an etching reagent between the outer circumference of the layer for the phase adjustment (314) and the internal circumference of the electrode of the annular shape at the (p) side (313) and then due to an occurrence of erosion of the contract layer of the (p+) type (312). Moreover, in such a case where the gutter (324) is formed, the contract layer of the (p+) type (312) has a thinner layer thickness or a rupture and a higher electrical resistance. As a result, the electrical current which is injected from the electrode of the annular shape at the (p) side (313) flows in a direction to a face in the electrical current path of the (p+) type (310) as arrowed with making use of an (Ar3) therein in place of flowing in a direction to the contract layer of the (p+) type (312), leading to an increased resistance of the element.
An objective is to provide a method of manufacturing a surface emitting laser element of a vertical cavity type and another objective is to provide the surface emitting laser element of the vertical cavity type with a lower threshold electrical current for emission.